The role of diagenetic studies in production operations

Abstract

A B S T R A C T : Petrographical studies can be undertaken to investigate the effects of production operations on sandstone reservoirs and to identify the nature of any rock-fluid interaction. In combination with diagenetic models the results may be employed to predict the effects of field development programmes on reservoir mineralogy, and to avoid costly damage to the reservoir's permeability. Acidization to remove drilling mud from Reservoir A samples was undertaken in two stages to avoid adverse rock-fluid interaction. HC1 dissolved siderite and chlorite but did not increase permeability. This is because the dissolved siderite released previously cemented clay particles into the pore space. A subsequent mixture of HCI and HF dissolved all the clays present in the treated area including the drilling mud, but also etched the quartz cement. Permeabifity increased significantly but the rock's strength decreased. This could cause an influx of loose sand during hydrocarbon production. Water injection into Reservoir B samples caused a variety of rock-fluid interactions. In finer-grained samples movement of siderite rhombs as well as clay particles blocked pores, and changes in porewater composition caused smectite to swell. Both effects caused permeability to decline. In the coarser-grained siderite-free samples, permeability improved after oil and clay particles had been displaced. In the reservoir these effects would combine to exacerbate the effects of the existing reservoir heterogeneity. Steam injection into Reservoir C samples caused mineralogical reactions. Amounts of dolomite and kaolinite decreased, and smectite and calcite were generated. This may affect the permeability of the reservoir and will determine whether oil can be produced through the affected sediment.

Clay Sedimentology

“…Kantorowicz et al (1986) investigate experimentally some of the reservoir-property modifications induced by production operations. After such processes, the remaining oil may be recovered by heating the oil to lower its viscosity, or by changing the properties of the injection water.…”

Effect of Kaolinite on Water-in-Oil Emulsion Formed by Steam Injection during Tertiary Oil Recovery: A Case Study of an Omani Heavy Oil Sandstone Reservoir with a High Kaolinite Sludge Content

“…The presence of kaolinite, illite, and/or dolomite (common clay found in sandstone) in sandstone reservoirs plays a major role in the success or failure of the steam flooding process. − In sandstone reservoirs, kaolinite clay minerals play a petrogenetic role that is still a matter of debate during the steam injection process . As a result of their large internal surface area along with the high salinity within oil reservoirs, they tend to react rapidly and easily .…”

Automated Rock Characterization With SEM/lmage-Analysis Techniques

“…Such studies provide information about controls on reservoir quality3,4 and rock/fluid interaction during drilling and production operations. 5 Quantitative or semiquantitative petrographic information requires more tedious and time-consuming manual procedures-e.g., point counting to determine mineralogy.…”